The Desire is pretty much the Nexus One inside a different case so I have a good idea what it's like.
Not quite then, and even more so now. The Nexus One has the blinking clickable rollerball thing while the Desire has the optical trackpad which doubles as a button. People seem to be split about which one is better usability wise. And for the Telus Desire, the screen is going to be SLCD instead of AMOLED due to supply problems. No idea how that compares to good old AMOLED yet, but the Galaxy S is using Samsung's own super AMOLED so I would think the edge will go to the Galaxy S.
Why sign yourself into a three year contract?
I could ask you people in the US the same thing about 2-year contracts - carrier subsidy. People in North America just don't get the true cost of a phone and are willing to get locked in to get their "free" or "cheap" phones.
What would be the possibility of buying the Galaxy S and unlocking it to work on the Telus network? They share the same CDMA/HSPA network, so I think it should work - but I never unlocked a phone before. At least I have a sim card now.
That, is the biggest question. I personally prefer the stock Android stuff or 3rd party non-carrier mods (I really like that Cyanogen one that my friend has on his Nexus One). Besides, who knows what the idiots at Telus will add to the phones to slow it down and/or burn battery faster. These Android phones are almost begging to be unlocked and modded (damn you AT&T). I would wait until the modding community has tested and documented a way to unlock/root the phones first before diving in.
As for the hardware itself, I have tried the Captivate (AT&T's Galaxy S) and it is pretty smooth. Though I think it is a touch slower than stock Android on the Nexus One. My friend also tried the Desire mod on his Nexus One and it is a bit slower too. So I am going to say Sense vs TouchWiz on their different CPUs is going to be a wash. Now, super AMOLED vs SLCD aside, the Galaxy S is huge with the 4" screen. For the few occasions I am actually agreeing with Jobs that it is getting a bit big for my own taste. To me it is becoming to turn into a "not a phone".
The Desire/Nexus One's 3.7" is about the maximum I can tolerate at this point. However, you may have already gotten used to the big screens for your smartphones so this may not matter for you.
The Model M is not for the faint of heart. You either like them or hate them.
Gerbils unite! Fold for UnitedGerbilNation, team 2630.